The complexity of optoelectronic systems is motivating the need for CAD tools which can simulate electronic and photonic device and circuit behaviors simultaneously and at multiple levels of abstraction. We describe such a tool, called AnaVHDL, which is being developed to concurrently simulate the behavior of optoelectronic systems consisting of digital, analog, and optical circuits. The approach is to extend the very high speed integrated circuit Hardware Description Language (VHDL) to describe the behavior of analog circuits and optical components, and to develop a simulation kernel which supports both discrete-event and continuous-mode simulation.